In WordPress Settings, the first four items you specify are Site Title, Tagline, WordPress Address (URL) and then Site Address (URL). Depending on how you created your site, the two addresses may already be filled out with the same URL.
So, what’s the difference between them?
The WordPress Address is where your admin pages are, along with all the other parts of WordPress, such as the folders “/wp-content/”, “/wp-include/” live. It is were the code or brains of your WordPress site reside.
The Site Address is the public-facing part of your site. It is the URL that visitors visit, and the URL you put on your business card.
Why are they sometimes different?
In a default WordPress installation, the two address are the same. But sometimes WordPress is in a different folder or directory than your public home page. Why? Here are a couple of the reasons why they may be different:
1) Your site has parts that are not WordPress based.
2) You want to keep your root directory free of WordPress folders and files.
If you currently have WordPress installed in your root folder, and want to move it to its own folder, the WordPress codex has instructions for that here: How to Give WordPress its own Directory.